Bring 1 cup blueberries, water, and 1 teaspoon sugar to simmer in small saucepan over medium heat. As it heats up mash your blueberries with a potato masher. They will break down and thicken as you cook them. It should reduce by about half. It will take about 5 minutes or so. Remove from heat and place in a bowl and put aside to cool while you prepare the rest of the recipe.

In a large bowl take flour, baking powder, and salt together and mix together with a whisk. Take remaining sugar and eggs and whisk together in medium bowl until thick and well mixed. Slowly mix in butter and oil until combined. Whisk in buttermilk and vanilla. Using a rubber spatula, fold egg mixture and remaining cup blueberries into flour mixture. Remember that with breads you don't want to mix a lot. Fold over just enough to combine ingredients. It's okay if there are lumps.

Take half the batter and place in the bottom of the bread pan (see picture above). Spoon the cooked berry mixture into center of the batter but don't let it touch the sides. Pour remaining batter over the mixture. Sprinkle lemon streusel mix over batter.

Bake until top is golden. Bake at 425 for 30 minutes and then reduce to 350 until cake tester pulls clean. (I checked in 10 minute increments) Once pulled clean let sit for 5 minutes then transfer to wire rack and let cool. To store wrap in tin foil and keep refrigerated.